1. Field of the Invention
The present invention relates to a probe for projecting measuring light to an organism and receiving output light from the organism through the measuring light for non-invasively measuring kinds of physical quantity of a vital tissue. This probe is used for irradiating, for example, a human body with light of a near-infrared region and measuring kinds of physical quantity in the human body such as a glucose concentration in blood, oxygen saturation of blood, body fat or an abnormal tissue by output light from the human body.
2. Description of the Prior Art
In the field of clinical testing, there is made an attempt of irradiating an organism with light and receiving the light penetrating into the organism to be scattered or reflected therein and outgoing from the organism for measuring an oxygen saturation in blood or a blood-sugar level or obtaining a body fat rate. There is also made another attempt of detecting an abnormal tissue from change of reflection properties responsive to the strength of a pressure by controlling the pressure pressing a probe for transmitting/receiving light to/from an organism against the organism.
As a first method of pressurizing a measured portion in measurement of an organism, a method of putting a cuff of a finger-blood-pressure-gauge on a finger and controlling an air pressure fed to the cuff thereby congesting a measured portion is proposed (refer to Japanese Patent Laying/Open Gazette No. 1-146525 (1989)).
As a second method, a method of slidably inserting an optical fiber bundle for transmitting/receiving measuring light into a tube and interposing a spring between the optical fiber bundle and the tube thereby pressurizing an organism with the optical fiber bundle through the force of the spring or introducing a transparent body for transmitting/receiving measuring light into a tube and pressurizing the same with an air pressure thereby pressurizing an organism with the transparent body is proposed (refer to Japanese Patent Publication Gazette No. 60-43134 (1985)).
The first method is limited to only measurements of a finger, and cannot be applied to measurements of a wide area portion of a human body.
In the second method, the pressure for pressing the optical fiber bundle or the transparent body for transmitting/receiving light against the organism can be controlled through the spring or the air pressure. However, the area of the forward-end-surface of the tube supporting the optical fiber bundle or the transparent body is small, and contact with the organism is mainly made on the forward-end-surface of the optical fiber bundle or the transparent body for transmitting/receiving light The area of this forward-end-surface is also small, and hence, only the measured portion is pressurized. Thus, it is difficult to stabilize the degree of application of the pressure to a portion around the measured portion.
When pressurized, an organism such as a human body may be congested or may lose a large quantity of blood depending on the degree of pressurization or influence by a contact area. In either case, reproducibility of the state as well as reproducibility of a result of measurement is reduced when the contact area is small.
Accordingly, an objective of the present invention is to improve reproducibility of measurement by keeping a degree of application of a pressure to a region including a measured region and its periphery.
A probe for optical measurement according to the present invention comprises a first optical component arranged on a central axis having a flat circular forward-end-surface and a second optical component having a flat forward-end-surface arranged in the form of a ring on a circle surrounding the central axis outside the first optical component, and these optical components are engaged with each other to be relatively slidable in the axial direction. One of the optical components is a projecting part projecting measuring light to a measured object, and the other optical component is a photoreceiving part receiving output light from the measured object through the projected measuring light The probe for optical measurement further comprises an outer peripheral part having a forward-end-surface in the form of a ring on a circle surrounding the central axis outside the second optical component, and the ring is formed to be larger in width than the ring of the forward-end-surface of the second optical component.
The projecting part and the photoreceiving part are independent of each other and the photoreceiving part is arranged to enclose the projecting part or the projecting part is arranged to enclose the photoreceiving part to the contrary, whereby information on a deep place of an organism can be readily obtained as compared with a probe having a projecting part and a photoreceiving part located on the same place as a transmission/photoreceiving part.
The wide outer peripheral part is provided outside the second optical component, whereby the degree of application of a pressure to a wide portion around the measured region can be kept constant by bringing the outer peripheral part into contact with the organism. A contact pressure in a narrow range of the measured region can be changed with the first optical component, whereby reproducibility of change of a tissue component such as change of a blood component in the measured region can be improved.
The output light from the measured object received by the photoreceiving part includes all light output from the measured object such as transmitted light, scattered light and reflected light after projection of the light to the measured object.
The outer peripheral part is integrated with the second optical component so that the forward-end-surfaces of the outer peripheral part and the second optical component can be flush with each other. Thus, measurement can be made in a state bringing the forward-end-surface of the second optical component into contact with the measured region along with the outer peripheral part.
The outer peripheral part is alternatively integrated with the second optical component so that the forward-end-surface of the second optical component may be located in a vertical position retracted from the forward-end-surface of the outer peripheral part Thus, measurement can be made in a state not bringing the forward-end-surface of the second optical component into contact with the measured region, for reducing influence exerted by the probe on the measured region.
The projecting part can be a light-guide-path guiding the measuring light from a light source. In this case, the degree of freedom in light source selection is improved, wavelength selection is easy and it is also easy to attain high luminous energy. It is also possible to provide a spectroscope between the light source and the light-guide-path.
The projecting part alternatively can be provided with a light emitting device such as an LED (light emitting diode) or an LD (laser diode) embedded therein. In this case, it is advantageous for miniaturizing the probe.
The photoreceiving part can be a light-guide-path such as an optical fiber bundle guiding the received output light to a detector. In this case, the degree of freedom in detector selection is improved. It is also possible to provide a spectroscope between the light-guide-path and the detector.
The photoreceiving part alternatively can be provided with a photoreceiving element such as a photodiode or a phototransistor embedded therein. In this case, it is advantageous for miniaturizing the probe.
When arranging the photoreceiving part to enclose the projecting part, it is possible to efficiently receive the output light from the organism, and detection sensitivity is improved.
In order to measure kinds of physical quantity of a vital tissue, light from near-infrared to infrared regions is preferable. The light source being used, emitting light included in such a wavelength region, may include a continuous spectrum of this wavelength region or discontinuous bright line spectra. Such a light source may be formed by an LED or an LD for near-infrared or infrared emission, in addition to a tungsten-halogen lamp.
The detector or the photoreceiving element has sensitivity to the near-infrared or infrared region, and such an infrared detector can be formed by a Ge photodiode, an InGaAs photodiode, a PbS photoconductive element, a PbSe photoconductive element, an InAs photovoltaic element or a pyroelectric element.
It is possible to keep a contact pressure on the measured region constant for improving reproducibility of a result of measurement by making the distance of relative projection or retraction of the first optical component in the axial direction constant with respect to the outer peripheral part. To this end, a mechanism slidably engaging and supporting the optical components is preferably provided with a stopper relatively positioning the optical components on such a position that the forward-end-surface of one of the optical components projects by a constant distance with respect to the forward-end-surface of the other optical component.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.